Description

Ferulated arabinoxylans (AX) are polysaccharides that form hydrogels by covalent cross-linking involving FA oxidation. AX gelation process and gel properties depend on AX structural characteristics such as molecular weight, substitution degree, and FA content and location. AX gels have potential application as delivery systems for biomolecules or cells and antioxidant activity. AX modification can be a path to tailor their properties and specific applications. Only a few reports have been carried out on the carboxymethylation of AX. The influence of carboxymethylation on the gelling capacity, rheological properties, and antioxidant activity of AX from different sources was investigated. Wheat flour arabinoxylan (AX1) and distillers dried grains arabinoxylan (AX2) were carboxymethylated. The success of the treatment was corroborated by Fourier-transform infrared spectroscopy. Unlike non-modified AX, the spectra of carboxymethylated AX1 (CAX1) and AX2 (CAX2) showed three new bands at 1594, 1418 and 1324 cm-1. The absorption bands at 1594 and 1418 cm-1 were assigned to C=O stretching of the COO- ion, indicating the presence of new carbonyl groups within the carboxymethylated species. Meanwhile, the absorption band at 1324 cm-1 was assigned to C=O stretching of the –COO- ion or to the symmetric angular deformation of the C-H bond. Size-exclusion chromatography analysis showed that the average molecular weight (Mw) of the samples was affected by the carboxymethylation. The Mw for CAX1 decreased from 729 to 591 kDa, while that the Mw for CAX2 increased from 130 to 145 kDa. These results indicate that the chains of CAX1 were susceptible to degradation while that CAX2 were not. In addition, it is possible to assume that the increase of Mw in CAX2 involves the introduction of new carboxymethyl groups. The rheological measurements demonstrated that AX1 and AX2 solutions formed gels. The storage modulus for AX1 gel was lower (G’= 71 Pa) than for AX2 gel (G’= 196 Pa), which could be attributed to a lower FA content in AX1 in relation to AX2. In contrast, the CAX1 and CAX2 do not gel (G’ < G’’); the release of FA from AX chains during carboxymethylation process could explain this result. The antioxidant activity of AX1, CAX1, AX2 and CAX2 were of 135 ± 17, 249 ± 7, 229 ± 10 and 283 ± 4 TEAC (mmol/ kg), respectively. The increase in the antioxidant activity of CAX1 and CAX2 in relation to the unmodified molecules could be related to the carboxymethyl groups incorporation, which increases the electronic cloud in the AX chains favoring the potential for hydrogen donation. Based on these results, the carboxymethylation of AX decrease its gelling capacity but increase its antioxidant activity, which could define the possible applications of these carboxymethylated materials in food, cosmetics, and biomedicine, among others areas.